The present invention relates to a light-sensitive polymer sensitive to far ultraviolet rays and suitable as a resist material for forming fine patterns of, for instance, semiconductor elements, a method for preparing the same and a method for forming such a pattern using the light-sensitive polymer.
Organopolysilanes, whose main chain is completely composed of silicon atoms, strongly absorb ultraviolet rays at 300 to 350 nm and thus shown sensitivity to ultraviolet rays. Moreover, these compound undergo oxidation with oxygen plasma to thus be converted to SiO.sub.2 resistant to oxygen dry etching. Therefore, it has been attempted to adopt them as the upper layer of a tow layered resist system in ultraviolet lithography techniques for manufacturing semiconductor elements or the like and its effectiveness has been proved empirically.
On the other hand, the dramatic increase in density and degree of integration of today's semiconductor elements strongly requires the development of a method for forming a pattern having a width of not more than 0.5 .mu.m. To form such a fine pattern, it is believed that the lithography technique relying on the exposure to ultraviolet rays is no longer ineffective and as a result, lithographic techniques utilizing electron rays, X-rays or far ultraviolet rays have been investigated. However, the technique comprising exposure to electron rays makes the formation of fine patterns easy, but leads to low throughput; while with respect to the technique comprising exposure to X-rays, there has not been developed any high-output source of X-rays and it is not expected to further enhance the sensitivity of resist materials. On the contrary, in the technique comprising exposure to far ultraviolet rays, all the existing equipment for a stepper can be employed by simply changing the light source and optical systems, and high-output sources thereof such as excimer lasers have already been developed. Therefore, the best possible lithography technique is one comprising the use of far ultraviolet rays.
An important subject which has remained unsolved in the lithography technique using far ultraviolet rays is to develop a single layered resist or an upper resist for two layered resist systems. As in the ultraviolet lithography, the use of organopolysilanes has been investigated, but the absorption at 300 to 350 nm which is important in the ultraviolet exposure inhibits the bleaching effect and lowers the contrast of the resultant pattern. Thus, there has not yet been developed any such materials effective in the far ultraviolet exposure.
Under such circumstances, there has been a strong demand for the development of novel light-sensitive polymers which contain silicon atoms, strongly absorb only far ultraviolet rays and thus exhibit sensitivity to far ultraviolet rays.